It is the goal of this study to define the role of the respiratory epithelium of the lung in the maintenance of fluid distribution across the barrier between blood and air. Several preparations, including the excised amphibian lung, the perfused, fluid filled rat lung lobe, the in vitro rat trachea, and an oil blocked, microlavaged terminal alveolar sac of the rat lung, will be examined. These preparations either restrict solute transfer to paths across the alveolar epithelium (excluding parallel routes through the airway epithelium) or estimate alveolar permeability from the differences between measurments from the whole lung lobe and the trachea (a model for the airway epithelium). The proposed studies with amphibian lung will extend our earlier work by examining nonelectrolyte, K ion, and Ca ions fluxes along with the effects of three groups of environmental pollutants (heavy metals, an ozone product and the dipyridilium herbicides) on bioelectric properties, solute permeability and biochemical indices of free radical production. Micropuncture and oil blockade of a terminal alveolar sac will allow measurement of the transalveolar bioelectric p.d. and solute permeability. Each result will be compared with the values for the alveolar epithelium that are predicted by difference from similar measurements on whole lobe and trachea. Effects of the selected pollutants on these parameters will be explored. Thus, a second objective of this project is to identify the locus and nature of pollutant damage to the air-blood barrier and to relate this damage to metabolic events in the epithelium.